Boride ceramics are of great technological importance primarily because of their hardness and wear resistance. They possess higher oxidation stability in gaseous and liquid reactive media than corresponding pure metals and alloys. Several fabrication methods are known to produce boride materials, such as sintering, hot pressing, plasma spraying of TiB.sub.2 powder or chemical vapour deposition. The production of bulk borides involves the use of expensive TiB.sub.2 powder. The sintering of TiB.sub.2 powder is usually done at 2000.degree. C. Oxide-boride composite ceramics have commonly been produced from ingredients corresponding to the crystalline phases in the composite: see for example U.S. Pat. Nos. 2,270,607, 3,067,146, 3,296,002, 4,022,584, 4,110,260 and 4,343,909.
Recently, U.S. patent application Ser. No. 454,671, T. de Angelis, as yet unpublished, has proposed an oxide-boride ceramic produced by reaction sintering whereby the ceramic consists essentially of a fine-grained, homogeneous interdispersion of 10-90 mole % of a boride phase and 10-90 mole % of an oxide phase. One example (body D) was a porous ceramic of titanium diboride and alumina of uniform grain structure (about 95 volume % of the grains of both oxide and boride phases were less than or equal to 7 micron while the largest grain was 10 micron) and with a density of 3.8 g/cc and 2.6% open porosity.